A more thorough explanation:

Definition: Main-rent is a term used in feudal times to refer to the service required of a vassal, or the territory held by a vassal. It is also known as vassaticum or vasseleria. Main-rent can also refer to the dominion or authority of a feudal superior over their vassals, or to political servility and subjection.

• A knight might owe main-rent to their lord in the form of military service or other duties.
• A vassal might hold a piece of land as their main-rent, which they would use to generate income and support themselves.
• The king's main-rent was the loyalty and obedience of his vassals, who owed him fealty and service in exchange for protection and support.

These examples illustrate the different ways in which main-rent was used in feudal society. Vassals were expected to provide some form of service or tribute to their lords, whether in the form of military service, labor, or goods. In exchange, they were granted the use of land or other resources to support themselves. The relationship between vassals and their lords was one of mutual obligation and dependence, with each side relying on the other for support and protection.